Diesel fumes impair blood vessels.

Breathing in diesel exhaust fumes at levels typically found in large cities disrupts important blood vessel functions, new research has shown, suggesting a potential mechanism linking increased heart attack rates during periods of high air pollution.

Numerous studies over the last 20 years have shown that the numbers of deaths and hospitalizations due to heart attack and stroke go up as traffic-induced air pollution rises.

The link between air pollution and cardiovascular disease is strongest for fine-particle pollutants, of which the combustion of fossil fuels from vehicles is a major source. Yet the underlying factors responsible for air pollution's effects on the heart and blood vessels had remained largely unknown.

The study led by Dr. Nicholas Mills, a researcher at the Centre for Cardiovascular Science at the University of Edinburgh, suggests what some of those factors might be.

Researchers found that exposure to diesel exhaust for one hour during exercise caused a significant decrease in the blood vessels' ability to expand, or dilate. Exposure to the air pollution also decreased levels of an enzyme that helps prevent clots from forming in the blood and possibly causing a heart attack.

"Low levels of diesel exhaust are having real effects on our blood vessels, and the way in which they function, that may potentially be sufficient to act as a trigger for a heart attack," Mills said yesterday from Edinburgh, Scotland.

Short-term exposure to air pollution can worsen existing problems and lead to hospitalization for heart attack and other heart and lung conditions. Long-term repeated exposure increases the risk of death from coronary heart disease, abnormal heart rhythms and heart failure.

"Long-term exposure could be contributing to the formation of coronary artery disease," said Mills, whose study is published in the Journal of the American Heart Association.